[Turnertech41]

Have a 25 ton intellipak, lost a comp shortly after a large refrigerant leak in July. Had to replace one condenser coil and compressor. Ran well until October the lost the same compressor again. Locked up, busted scroll. Replaced, as well as LLD and contactor. Recharged with factory charge weight 55#. All vitals looked good. Ran a a month and dropped it again, rinse and repeat. Checked everything on tracer SC, have VAV mins @ total of 4100 CFM, 20% outdoor air, medical facility. Did find low ambient fan actuator with stripped gears and failing, superheat at 10* both comps running, 5* SH with a single comp running. Supply static 1.6”. Noticed every few cycles the compressors would start hard with liquid flooding for a few seconds then smooth out. We suspected TXV sticking. CCH are working. Replaced TXV and another compressor, this time compressor 1 the 10t on the tandem, that’s the first time it’s been changed. Even after new txv still have flooded starts, adjusted txv to maintain superheat around 16-20* depending on one or both comps running. I have no idea what’s causing the flooded starts! The building had a low load, single duct VAVs with HW reheat. I know the return is a little undersized, but it’s been running without hick up for 10 years.

Suction restrictor is the correct size and is in correct compressor.

These compressor failures are never electrical, it’s always lock rotor, one was bad enough to have dents poking out of compressor shell.

 

[slctech]

Possibly oil issues? Too much and it is causing havoc?

 

[Turnertech41]

Kind of wondering that at this point. At times when just 1 compressor is running, it’s sightglass is full the other is down at bottoM of sight glass. If both are running their both 3/4 full or better, if both are off they’re both full.

 

[slctech]

Usually the first failure leads to oil trapped in evap, then new compressor added with none of the oil removed, then the second, then the third, and just oil slugs now moving through the system brutalizing the compressors.

Usually what happens is the oil will build up and log the inlet of the TXV, starving the evaporator. The TXV starts opening to feed more refrigerant to the starving evaporator and that slug of oil that was causing the issue is now allowed to grunt through and head straight for the compressor.

Not saying this is the issue, but something that is overlooked after numerous compressor changes.

 

[71CHOPS]

I would say slc is correct, too much oil. With those compressors OFF, after about 5 minutes, you should see about 1/2 glass. I'd it's full, you have too much.

I would also say, with that many compressors changed, there is so much oil that you're likely not.gsttimg accurate readings.

You did well with 16-20* SH with one or all compressors on. That's a good place to be...I don't set them below 15*.

Get a 50lb. Recovery cylinder, put it on a scale, run your liquid line hose to the liquid side of the cylinder, then run your vapor side of the cylinder back to the suction line. Watch your weight and pressures, as you fill the tank, meter rhe vapor side to maintain a fairly steady weight (but increasing) weight. Sometimes you,ll have to stop the liquid feed to let it "catch up". You can remove oil this way with the system running.

A faster way is to connect your recovery cylinder directly to the oil fill port on the compressor. Get your cylinder in a vacuum, run the system, shut it down. After about 5 minutes, open the calves to the tank, ans just suck out of the sump.

A combination of those tactics will give good results.

I remove 16 lbs of oil from a 75 ton I-pak once. You'll likely have to adjust the charge when you're done.

 

[ehsx]

Check corrected txv sizing for application. Sporlan & Alco valves typically have 30% of corrected capacity turndown. Sized correctly ssh should be same with one or both compressors.

Unit have liquid line solenoids and pumpdown.?

Test loaded and unloaded suction and discharge sh. Low discharge sh indicates oil flooding back if ssh is good.

 

[VTP99]

I didn't see anything mentioned about a suction line filter.
Doesn't Trane want both compressors replaced when in tandem ?

 

[ehsx]

Suction line filters can be compressor killers if not installed correctly, downflow vertical or downflow diagonal only.

If rotor lock connections, no acid or severe contaminates changing one is ok. Otherwise would change both.

 

[VTP99]

Yeah on a mechanical failure I'd be concerned about all kinds of crap moving thru that system.

 

[Ray7129]

Ive witnessed this same issue before when using a DX system for VAV's. Im going to assume the compressor that keeps going out is the 1st stage. What may be happening is the logic running system is toggling that stage on and off repeatedly. We also found that the system needed hot gas bypass for low load times. After adding HGBP and implementing long time delays between staging up and down, our problems went away.